Conventionally, in a pneumatic tire for winter season, a block pattern has been most commonly used as a pattern of a tread section. For example, as shown in FIG. 5, relatively large blocks of substantially the same size are demarcated by main grooves and lateral grooves, which grooves serve to generate a snow column shearing force and the like so as to improve on-snow performance, and sipes are formed in the tread blocks so as to improve on-ice performance (see Patent Document 1).